The ~3000 m deep GISP2 core will yield a high resolution, ~200,000 year history of global change - to include two interglacials and two glacials - the longest such record available from the Northern Hemisphere.The Global System
During the past decades, linkages between the atmosphere, biosphere, anthrosphere, hydrosphere, cryosphere, lithosphere and cosmogenic input have been revealed. These linkages are characterized by complex integration and feedback. While the existence of this complex global system is now recognized, how it functions is poorly understood. The recent increase in CO2 and other greenhouse gases as a result of human activity and in turn concern over the climate change which may result require that we gain a detailed knowledge of the total global system. The history which will be derived from the GISP2 core will provide the detailed record of interaction needed to unravel the functioning of the global system. Further, the wealth of this history will help to fuel the next generation of visionary thought in Earth System Science.Global System Signals
Signals which are generated by interactions within the global system can be seen in the atmosphere, "captured" in the cryosphere and are available for our viewing by the sophisticated analyses of ice cores. Properties which will be studied in the GISP2 core include: Gases, stable isotopes of occluded gases, stable isotopes in ice, particles, major and trace element chemistry of ice, cosmogenic isotopes, conductivity, physical properties.Global Change
The detailed view of global system history revealed from these ice core properties will expand significantly our understanding of global change- EVOLUTION, PROCESS, TREND, AND COHERENCE. It will provide the type of PERSPECTIVE necessary to assess PREDICTIVE global change models. Specifically, a GISP2 global change history will include:
*GISP2 is comprised of scientists from: the Cold Regions Research and Engineering Laboratory, the Desert Research Institute, Ohio State University, Pennsylvania State University, the New York State Department of Health, the State University of New York at Albany, Lamont-Doherty Geological Observatory, University of Arizona, University of Colorado, University of Miami, University of New Hampshire, University of Rhode Island, University of Washington and the University of Wisconsin under the scientific management of the University of New Hampshire and with logistic and drilling support from the University of Alaska in Fairbanks.
Continuous visual logging of the core, systematic measurement of density, texture, (size, shape and arrangement of grains and pores) and fabric, (crystallographic orientation), and detailed study of these properties in especially interesting intervals. The first such detailed study is now being investigated. The results of this research will provide the necessary physical framework in which to interpret the paleoclimatic record in the core, important data needed to understand ice dynamics, to date the core by flow modelling, and improve understanding of the physical properties and processes of ice as a material and as part of an ice sheet.
Specifically this study will verify the validity of paleoclimatic and other results from GISP2 through study of the physical properties of the core. Physical processes during formation and flow of glacial ice and recovery and relaxation of ice cores can affect the stratigraphic record of trace impurities profoundly under some circumstances; such effects must be characterized or demonstrated to be negligible to validate paleoclimatic analyses.
This study will also advance our understanding of the formation and behavior of glacial ice. Ice is a widespread and economically important material. It is central to glacier dynamics (and thus to ice-sheet stability and future sea levels), and can be used as an analog for geological (mantle creep) and engineering (hot pressing, high temperature creep) processes. Fundamental physical knowledge gained from ice-core studies is thus of considerable value; such knowledge also can be used to improve the ice-dynamical time scale and thus the interpretation of paleoclimatic data.Data Management
The d18O of atmospheric O2 is influenced by d18O of seawater (the ultimate source of all photosynthetic O2), isotopic fractionations during photosynthesis, respiration, and hydrologic processes. They thus reflect the changing nature of planetary interactions between the biosphere, hydrosphere, and atmosphere (Fireman and Norris, 1982; Horibe et al., 1985). Further, the curve of d18O (O2) vs. time indicates the rate of primary productivity on the planet, as well as relative rates of primary production in the oceans and on land. We also propose to use d18O of O2, which is constant throughout the atmosphere at any one time, as a time-stratigraphic marker for the correlation of Greenland and Antarctic ice cores.
Results of our studies to date, extending back to about 30 kyr B.P., indicate that the O2 content of the ice ace atmosphere was about 8% less than at present. We propose to check our existing results with additional measurements, and to extend the record back to 200,000 years before present. We will use the results to test, or generate, hypotheses explaining the causes of glacial/ interglacial changes in the atmospheric CO2 content. The N2/Ar ratio of ice core trapped gases provides for a test of sample integrity. The atmospheric concentrations of N2 and Ar in air cannot have changed significantly during the last few million years, because these gases are relatively inert and consequently have very long atmospheric turn-over times. Absent any physical fractionation of gases, the N2/Ar ratio in ice core trapped gas samples will be identical to that in the modern atmosphere. Differences would indicate that physical fractionation processes have changed concentrations of the gases trapped in the ice, including those which are radiatively active. The results will provide a boundary condition on the reliability of radiatively active gas concentrations, to be measured by other investigators in samples from the GISP2 core.
Work from our lab shows that the isotopic composition of N2 and O2 in ice core trapped gases differs from that of modern air, due to mass-dependent fractionation during the gas trapping process. This fractionation would affect concentrations as well as isotopic compositions of all constituents in trapped air. A fractionation correction, based on the d15N of N2 in the trapped gas can and must be made for all isotopic analyses of trapped gases.Origins of Particles in GISP2 Ice
The recently drilled GISP2 (Greenland Ice Sheet Project 2) ice core contains a wonderfully detailed record of paleoclimate, including a record of large and abrupt variations in atmospheric dust, back through at least the last glacial cycle. This dust contains the best -- and possibly the only -- record of net air mass transport pathways, if the continental source of the dust, its provenance, could be determined. We have been using several natural tracers to study the origins of deep-sea and lake sediments and atmospheric dusts for up to thirty years, and propose applying these techniques to study the origins of the dusts in the GISP2 ice core. If the mineralogical, isotopic and pollen tracers can be used to determine dust provenance, with the possibility of provenance changing from one climate regime to another, this would place extremely useful constraints on the modeling of atmospheric paleocirculation.
We have done some preliminary work on several pilot -study ice core samples from the last glacial maximum (LGM), and have found significant mineralogical variation -- indicating a southward shift in dust source area if the order of 10o latitude -- between samples from a lower-dust, interstadial period and a higher-dust, stadial period about 700 years apart. We have found just a few pollen grains that are consistent with this result, and are confident that we will also see significant changes in isotope compositions of the aluminosilicate minerals ( 87Sr/86Sr and e Nd(0) ) to further resolve the source areas. We have also found soluble minerals in the solid aerosol dust -- calcite and gypsum -- and propose extracting and isotopically analyzing these minerals( d34,d180,d13C and 87Sr/86Sr ) to add additional potential isotope tracers to the determination of dust origins.
We propose applying these tracer techniques to the varying concentrations of GISP2 dusts deposited during the period from the Older Dryas to the Pre-Boreal, and to the varying dust concentrations deposited during the stadials and interstadials from Interstadial 8 to 4 i.e., the interval between the ice-core equivalents of the H4 and the H3 deep-sea sediment Heinrich Events (bond, et al., 1993).Central Greenland Glaciological Survey
The Central Greenland Glaciological Survey was begun in 1987 and completed this field season (1989). A 150 x 150 km grid was established the first year, centered at the Summit camp (37¡ 55' W, 72¡ 18' N), and survey markers were installed at 20 sites. Using Doppler satellite surveying methods, positions were measured in both 1987 and 1989, thus enabling the larger scale pattern of ice flow to be determined. At 9 sites around the grid (which straddled the ice crest), shallow cores to about 17 m depth were recovered. The oxygen isotope stratigraphy, along with measurements of gross beta activity, has enabled the mean accumulation rate of the past 30 years or so to be calculated at each of the 9 sites. In addition, these detailed records are being studied to assess the spatial correlation in the isotopic signal. Measurements of deuterium and oxygen isotope variation in pit samples taken from the drill sites may enable specific source areas for precipitation to be identified. Also, the mean annual temperature (i.e., the temperature at 10 m depth) was measured this field season at a number of sites. This temperature field, along with the spatial distribution of accumulation rate and velocity, are fundamental parameters needed for realistic numerical models of ice sheet flow in Central Greenland.Helium and Rare Gas Studies
This proposal is for the measurement of helium concentrations and isotope ratios, Kr, Ar ratios, and Krypton 81 ages in ice from GISP2. The helium program is a search for nulls and/or reversals of the Earth's magnetic field, which should leave a strong signal in the helium 3 to helium 4 isotope ratios and the helium 3 concentrations in ice-core helium. Although the diffusivity of helium in ice is about the same as in liquid water, model calculations show that the signal should be well-preserved because of the high vertical advection velocity of the ice relative to the helium diffusion rate. The Kr/Ar ratios in Greenland ice down to ca. 150 meters depth are enriched relative to the ratios in air about 1.3%, and the ratio of this enrichment to the isotopic enrichment in nitrogen shows that the effect is due to gravitational equilibrium in the air column in the firn. The magnitude of these enrichments is about 85% of that calculated from the firn depth and temperature, probably because of turbulent mixing in the uppermost 10 meters of firn. The Kr/Ar enrichments may vary with depth, and it is proposed to measure the ratio on gas-splits from the helium samples collected. The helium samples must be collected in the field immediately on core retrieval because of the high diffusivity of helium in ice
If a geomagnetic helium event is recorded in the ice sheets, it will provide a world-wide traceable horizon in both Greenland and Antarctica, for chronology and for model studies of ice flow, using the known diffusivity if He in ice and modeling the tracer horizon in two dimensions. Moreover, the event can be correlated with the sedimentary record and with lava flows during the past 100,000 years. There are at least six possible events to look for: the Blake and Laschamp known events, the proposed Mono Lake and Lake Mungo excursions, and in addition, two Be 10 possible events observed in the Vostok core, that may in fact be markers of geomagnetic events.
Krypton 81 (half-life =213,000 years) is the only choice for dating ice older than 50,000 years. We have just reported the first Krypton age on ice, measured on 224 Kg of ice from the Allan Hills. The age was measured on 9000 Kr-81 atoms concentrated from an initial 90,000 atoms: the value obtained is 108,000 years with an uncertainty of 28,000 years. We have every hope that the amount of ice required will come down to some 50 Kg or less, and that the precision will increase, and it is hoped therefore to measure ages on two deep (>2500m) GISP2 samples.Atmosspheric Radionuclides at Summit, Greenland
This project will include atmospheric radionuclides among the species being measured at the solar-powered atmospheric camp(ATM) that was established in 1989 near Summit, Greenland as part of the Greenland Ice Sheet Project Two(GISP2). The PI will determine the concentrations of 7Be and 210Pb (and perhaps gamma emitting anthropogenic radionuclides) in high volume aerosol samples (collected continuously during the field season at a nominal 24 hour interval) and fresh and aging surface and near surface snow samples. 10Be and 36 will be measured in these samples by Dr. Robert Finkel (Lawrence Livermore National Laboratory) at no cost to NSF.
All of the research at ATM has the primary goal of fostering the interpretation of paleoatmospheric and paleoclimatic signals recorded in the ice of the Greenland Ice Sheet. This will be accomplished by improving our understanding of the current day transport proceeded, air-snow transfer processes, and early post-depositional mechanisms resulting in the incorporation of atmospheric constituents into the snowpack. Preliminary results indicate that measurements of the atmospheric radionuclides in the atmosphere and snow near Summit will illuminate the importance of atmospheric boundary layer dynamics, and post-depositional modifications of the snow, on the delivery and subsequent preservation of submicron aerosol-associated species in the region. Under the provisions of the GISP2 data exchange agreement, the results of this study will combined with those of other researchers at ATM (as well as various fresh and aging snow studies ongoing as part of GISP2) in a collaborative effort to begin to quantify the fidelity with which polar snow and ice record signals from the overlying atmosphere.Physical and Structural Properties Anthony J. Gow; Cold Regions Research and Engineering Laboratory
This program will investigate the stratigraphy, relaxation characteristics and crystalline structure of ice core. Studies will include: 1) delineation of annual layering to as great a depth as the visible stratigraphy can be deciphered 2) precision density measurements to monitor the relaxation characteristics of ice cores as they age 3) determination of the principal mechanisms by which cores relax-bubble decompression, fracturing, microcracking and exsolved gas cavitation, and complementary measurements of total gas volume in the ice and gas pressure measurements inside original bubbles and exsolution cavities 4) crystal size measurements as a function of the depth and age of the ice 5) c-axis fabric measurements and 6) analysis of debris in basal ice cores. Relaxation of ice cores results in significant changes in their mechanical condition that must be considered in relation to the preparation and analysis of core samples for entrapped gas and chemical studies; c-axis fabrics constitute the primary source of information for interpreting the strain history of the ice column that vertically drilled cores represent. Careful documentation of these key properties is essential to accurate assessments of the depth-age relationship and confidence in paleoclimate reconstructions based on geochemical and entrapped gas analysis.Oxygen Isotopes
The 18O/16O ratio of the ice in a core through the central part of the Greenland ice sheet provides a uniquely detailed record of paleoenvironmental conditions that may extend back as far as 200,000 years.
The 18O/16O ratio will be used to determine the characteristics of the major global climate cycles and the cause and effect relationships between the various environmental parameters, such as temperature, concentration of CO2 and CH4, dustiness, and cation/anion concentration, that change with climate. A better definition of the processes that determine climate change will provide better predictions of future climate change. To locate intervals of major and/or rapid climate change, that will be the focus of detailed multiparameter studies, we will use a preliminary isotope stratigraphy of the core.
The interpretation of the 18O/16O core record will be based in part on detailed observation of the 18O/16O in freshly fallen snow and in the near-surface firn near the Greenland summit drill site. The fresh snow 18O/16O and its changes during firnification will be matched with local weather and long-range air circulation data.
A special collaboration with J. W. C. White (D/H) will provide a record of deuterium excess("d").Determination of the Surface and Bed Topography in Central Greenland
The surface and bottom topography of the central Greenland ice sheet was determined from airborne ice radar soundings over a 180 x 180 km grid centered on the 1974 "Summit" site (37¡55'W, 72¡18'N), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high quality radar data were obtained, covering over 99 percent of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft's radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12 percent of the grid).
The highest point on Greenland is at longitude 37¡38'W, latitude 72¡34'N, at an altitude of 3233±6 m above sealevel. The ice in most of the southwest quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sealevel. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10-15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the southwest basin would be suitable for the drilling of a new deep ice core.The highest point on Greenland is at longitude 37 38'W, latitude 72 34'N, at an altitude of 3233+-6 m above sea level. The ice in most of the southwest quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10-15 km wide and extending about 50 km to the west. Major Anions and Cations, Total Acidity, and Ionic Balance
The major chemistry contained in the GISP2 core will provide a detailed view of the last ~200,000 years of paleoenvironmental history including characterization of: the chemical composition of the remote atmosphere; transport pathways, input timing and sources of the major chemical species in Greenland snow; volcanic events and their effect on the remote atmosphere; local precipitation balance; sea and land ice extent; dustiness of the atmosphere; biospheric influences; and, the signature of anthropogenic activity on the remote atmosphere. Time-series of chemical records will be evaluated for both episodic and cyclical signals.
Collaborative efforts within GISP2 will be geared toward defining the physical controls on chemical species depositon and the relationship between air and snow chemistry.
Chemical results will be placed in the context of local and intra-Greenlandic surveys of major snow and ice chemistry collected as part of this study. In order to interpret the local, regional, hemispheric, and global signatures found in the GISP2 paleoenvironmental record, the resultant data set will be viewed in conjunction with other global change records.Chemical Analysis, Morphology and Grain Size of Insoluble Particles
The insoluble particulates in selected samples from ice cores retrieved from the GISP 2 drilling effort will be analyzed for mass, concentration, size distribution, chemical composition and morphology. Sampling will be coordinated with investigators working on other analytical techniques (specifically ECM/laser particulates and ice chemistry) in order to identify the most important sections of the core for detailed study.
The insoluble particulate concentration of ice samples from the GISP 2 core will provide important information about not only the particulate loading of the atmosphere in the past but also temperature, radiation balance, global aridity, wind strength and circulation patterns.
Superimposed upon the "background" concentrations of continental dust associated with changes in climate will be elevated particle concentrations from sporadic events such as volcanic eruptions and perhaps extraterrestrial influxes of micrometeorites. Ice samples from core sections suspected of being associated with such events will also be examined in detail.
In addition to providing information about the temporal variations in the concentration and types of particulates deposited on the Greenland ice sheet, this study, in conjunction with others, should also provide insight to the relationship between volcanism and climate.
Further, because many of the most explosive eruptions in the past have occurred in the equatorial regions, the potential of using volcanic ash layers for inter-hemispheric ice core correlations seems very promising.Biogenic Sulfur and Iodine
The primary focus of this work is on methanesulfonic acid (MSA), an atmospheric oxidation product of dimethylsulfide. In conjunction with measurements of non-seasalt sulfate and sodium, the MSA data will allow us to assess the variability in the biogenic sulfur signal, and to differentiate between the oceanic source and sulfur from volcanogenic and anthropogenic emissions. The MSA record will be examined: 1) in detail over the last thousand years to assess anthropogenic impact to the sulfur cycle, and 2) over longer time scales in order to assess the relationship between the biogenic sulfur source and major climatic and atmospheric chemistry changes during glacial/interglacial cycles.
In the natural atmosphere iodine, like sulfur, is dominated by oceanic sources. The distribution of iodine species in the ice may, therefore, contain a potential tracer for the intensity of oceanic emissions from the ancient ocean. Our work will involve the development and refinement of new analytical techniques and the measurement of iodide and iodate concentrations in Greenland aerosols and ice. These data will provide the first information regarding the speciation and temporal variability of iodine in the high atmosphere and in polar ice.Greenland Automatic Weather Stations
The three automatic weather station (AWS) units installed on the Greenland crest in June 1989 measure wind speed, wind direction, relative humidity, and air temperature at a nominal height of 3.9 meters, air pressure at the electronics enclosure, and the air temperature difference between 0.5 m and 3.9 m. The units installed at GRIP and GISP2 also measure solar radiation and snow temperatures at +.20, -.05, -.30, -.55,-1.05, -2.05, and near -4.05 m. The Cathy site unit was installed at the Atmospheric Sampling Camp (ATM) and measures the distance to the snow using an acoustic depth gauge. The climatic objectives are: (1) to measure the present climate at each site so that possible differences around the crest will be known; (2) to measure the temperature profile in the first 4 m of the snow and to detect possible water vapor transfer. The meteorological objectives are: (1) to estimate the sensible and latent heat fluxes from the snow surface; (2) to measure the vorticity and divergence of the surface air motion around the crest; (3) to describe the possible katabatic wind around the crest; (4) to provide meteorological data for use in weather analysis and forecasting. The data are updated at 10 minute intervals and transmitted at 200 second intervals to the Argos data collection system on the NOAA series of polar orbiting satellites. The data are received at monthly intervals and available as 3 hourly values on paper, IBM format 3.5" and 5 1/4" disks, and as a complete data set on magnetic tape.Greenland Automatic Weather Stations
The three automatic weather station (AWS) units installed on the Greenland crest in June 1989 measure wind speed, wind direction, relative humidity, and air temperature at a nominal height of 3.9 meters, air pressure at the electronics enclosure, and the air temperature difference between 0.5 m and 3.9 m. The units installed at GRIP and GISP2 also measure solar radiation and snow temperatures at +-.20, -.05, -.30, -.55, -1.05, -2.05, and near -4.05 m. The Cathy site unit was installed at the Atmospheric Sampling Camp (ATM) and measures the distance to the snow using an acoustic depth gauge. The climatic objectives are: (1) to measure the present climate at each site so that possible differences around the crest will be known; (2) to measure the temperature profile in the first 4 m of the snow and to detect possible water vapor transfer. The meteorological objectives are: (1) to estimate the sensible and latent heat fluxes from the snow surface; (2) to measure the vorticity and divergence of the surface air motion around the crest; (3) to describe the possible katabatic wind around the crest; (4) to provide meteorological data for use in weather analysis and forecasting. The data are updated at 10 minute intervals and transmitted at 200 second intervals to the Argos data collection system on the NOAA series of polar orbiting satellites. The data are received at monthly intervals and available as 3 hourly values on paper, IBM format 3.5" and 5 1/4" disks, and as a complete data set on magnetic tape.Electric Conductivity Measurement
The objective of this proposal is to assist in the climatic interpretation of the GISP 2 core by measuring its electrical conductivity as a function of depth. This will allow a time-depth relationship to be developed for the core, and permit sampling by other investigators to be more efficient because of advanced knowledge of the core's gross chemistry.
In addition, the existence of long-term climatic trends and oscillation will be investigated. Results from the first year of the GISP 2 program show that a vertical resolution of 2 mm is possible; this will permit resolution of annual layers to an age of approximately 30,000 B.P. In ice older than 30,000 years, annual resolution will be lost but longer term events will be detectable. The objective of this proposal will be met by measuring the electrical conductivity of the core with a vertical resolution of 1 mm. The data will be digitally recorded so that digital processing will be possible. Preliminary results from the 1989 GISP 2 field season demonstrate the effectiveness of the method. The results of this proposal, combined with the other aspects of the GISP 2 program, will enhance our understanding of the earth's paleoclimate and ongoing climatic processes.CO2/Air Ratios and d13CO2
Air in bubbles of polar ice allows us to study the composition of the earth's atmosphere in the past. The records of the atmospheric trace gases contain information on how atmosphere,oceans and the biosphere operate and interact during different periods of the climatic cycle. The radiatively important CO2, part of the global carbon cycle, is of special interest.
The GISP2 core will produce very old ice and paleoclimatic information with excellent time resolution, due to the prevailing accumulation rate and mean annual temperature. We propose to establish in this core a high resolution CO2 record, which is necessary to ultimately understand the natural disturbances in the carbon cycle, and the relationship and interaction between CO2 and climate. After a survey, we will produce a high resolution CO2 record (by dry extraction on small samples, followed by tunable diode laser spectroscopy of CO2) over the main climatic periods (Holocene, transition and Younger Dryas, glacial including Dansgaard-Oeschger variations, glacial/previous interglacial, previous interglacial, and possibly beyond). This record, when compared to temperature records (and particulate/chemistry/cosmogenic isotope records) will yield information on the cause/effect relationship of CO2 and climate, and on the mechanisms to produce atmospheric CO2 variations over different time scales. If the rapid variations in the last glacial could be confirmed, important information would be obtained on the climatic consequence of the anthropogenic alterations to the earth's trace gas inventory in recent times. For periods of changing CO2 concentrations we propose to measure d13CO2 in detail. The carbon isotope ratio and its change in time can be used to define the mechanisms and scenarios which are responsible for atmospheric CO2 concentration changes. d13CO2 will be done by dry extraction technique and isotope ratio mass spectrometry, with appropriate corrections for the possible interferences.dD and Deuterium Excess
This study will measure and interpret stable hydrogen isotope ratios (dD values), and in collaboration with P. Grootes (d18O), interpret deuterium excess values. dD and d18O values in ice cores change in response to changes in paleotemperatures, in the rate of snow accumulation, and in the elevation of the ice sheet at the core site. dD and d18O values are also useful in counting annual snow layers during the Holocene, and thus allow dating and determination of accumulation rates during this period. Deuterium excess values are used to reconstruct evaporation conditions over the ocean, to interpret d18O values, and to infer historical shifts in the moisture source regions over the ocean.CO2 Isotope Ratios
This study will extend the atmospheric CO2 concentration and isotope composition record back through Holocene times. Measurements will be made in relatively small (250 g) samples of ice. The analysis is completed by placing the sample in a specially designed vacuum system where the ice is sublimed onto the surface of a -80¡C cold trap. The gas released by this procedure is passed through a multi-pass trap held at liquid nitrogen temperature which enables all the carbon dioxide to be recovered. The amount of CO2 sample so obtained is accurately measured and its 13C/12C ratio determined. The analyses will be made on ice samples which have also been 14C dated. The amount of air, per unit of ice, will record the altitude of the ice sheet at the time of seal-off. The ratio of CO2 to air will be accurately measured (to better than 0.15%) which will record the CO2 concentration of the sample of the trapped atmosphere to better than 1 ppm.
We will also measure accurately the 13C/12C ratio of atmospheric carbon dioxide during glacial times. The change of this ratio during the glacial/post-glacial transition will be an important test of the proposed mechanisms for the large CO2 concentration change that occurred at that time. Other climate-related questions that we will investigate include a detailed study of the end of the last glacial and the glacial/post-glacial transition, the Younger Dryas event, and the Dansgaard-Oeschger events. These concentration and stable isotope data, combined with radiocarbon dates for CO2, will enable testing of carbon cycle models relating to past and future climatic change.Tephrochronology Of The GISP2 Ice Core
Establishing a well-dated record of past volcanism is essential in determining the climatic impact of volcanism particularly on the decade to century time scale. Not only is the existing paleovolcanic record, especially in prehistorical time, incomplete, but the radiocarbon-based chronology during the Holocene and early Pleistocene results in a low-resolution record due to errors associated with the dating method. The direct deposition of volcanic debris on polar ice sheets provides the most reliable means of developing a more complete high-resolution record of volcanism. However, the chemical or acidic records of volcanism developed from ice cores do not directly provide evidence of the source volcano responsible for the ice core signal. The GISP2 ice core will be continuously sampled by standard petrographic techniques to locate and identify volcanic glass over the length of the core and particularly over the 100,000 year record available at an annual resolution. More detailed sampling by scanning electron microscope and electron microprobe together with ion microprobe analyses on selected samples will provide information on the major oxide and trace element composition of individual shards that may then be matched to a suspected eruption. Such matches will verify the source volcano responsible for the ice core signal.
In addition to establishing a more complete record of paleovolcanism, the results from this proposed study will provide important information on the extent of volcanism over several different time periods including changes in the temporal variability of explosive volcanism through the Holocene, the last glacial/interglacial transition including the Younger Dryas, stadial/interstadial transitions during the last glacial period, and during the Stage 4-5 transition. Data on the timing of volcanism during these time periods can provide critical information to assess the link between not only the climate forcing component of volcanism on the decade to century time scale, but also the role of climate change (i.e., deglaciation) on forcing volcanism. Other key components of this study are: 1) establishing a tephra record at the high-temporal resolution of the GISP2 core will provide a tie-line for all other ice core work and particularly future tephra work on ice cores, 2) distinguishing the importance of local and regional volcanism to the chemical record contained in the GISP2 core, especially the influence of Icelandic volcanism and possibly volcanism directly upwind (Kamchatka and Alaska), and 3) determining the magnitude of background tephra in the atmosphere and the residence time of tephra from known eruptions over primarily the last 300 years. Identifying the source volcano for existing chemical and electrical records of volcanism in the GISP2 core, and other ice cores in general, will be a critical step toward developing the most reliable record of paleovolcanism with the lowest possible dating error that now exists. Although not all the tephra located will be readily matched to a known eruption, this study will provide a data base of the age of tephra deposition of a known composition that will be available for use by volcanologists and other researchers interested in the atmospheric and climatic effects of volcanism (i.e., modelers). This study will complement a proposed study to evaluate the spatial variability of the tephra record for a series of cores across the Arctic region and in Antarctica with time-scales ranging from hundreds of years to records through the Holocene and Holocene/Pleistocene transition.Carbon Dating
Carbon-14 dates of atmospheric gases trapped in relatively small (a few kg) samples of polar ice cores will be determined. The atmospheric gases other than CO2 (and N2O) will be trapped on a molecular sieve and be available for other studies.
Personnel paritcipating in the 1989 field season included:The 109th New York Air Guard
4. Graphics 1. Surface and Bedrock maps Figure 2. Surface topography of the Summit region of the Greenland Ice Sheet. Map by S. Hodge et. al. in review. The S mark at grid position x = +9.4 km and y = +31.2 km marks the true summit of the ice sheet with a position of 37¡ 38' W, 72¡ 34' N. The S mark at grid position x = -18.0 km and y = +31.7 km marks the GISP2 camp and drill site with a position of 38¡ 27' 37" W, 72¡ 34' 38" N. The dashed lines indicate the nominal flight lines used in the mapping survey. Contour interval = 2 meters. Figure 3. Bed topography of the Summit region of the Greenland Ice Sheet. Map by S. Hodge et. al. in review. The S markers represent the same positions as in Figure 2. Contour interval = 20 meters. Figure 4. Surface topography map of the Summit region of the Greenland Ice Sheet showing full extent of the surface strain net survey. Map by Hodge et. al. in review, positions of geoceivers by John Bolzan. The large + is the true summit (x = +9.4 km and y = +31.2 km ), grid zero (x = 0.0, y = 0.0) is the 1987 Summit camp geoceiver station, and the small x's are the strain net geoceiver stations placed by John Bolzan. Contour interval = 4 meters 2. Photographs Picture A. Jack Dibb (UNH) checking solar generated power supply in "battery trench" at the Atmospheric Sampling Camp. Photo: M. Twickler. Picture B. Snowpit samplers in clean garments. Photo: P. Mayewski. Picture C. Science trench workstations. Samplers in clean garments. Photo: P. Mayewski. 3. ECM trace Figure 1. Preliminary Electroconductivity (ECM) trace by: K. Taylor, (Desert Research Institute) displaying seasonality and volcanic events.Tarumani, Japan and Katla, Iceland are volcanic events identified in the ECM trace which covers the time period from 1658 AD to 1669 AD. 5. Greenland Location Map? 5. November Meeting On November 1 and 2 there will be a meeting of the GISP2 investigators at the University of New Hampshire in Durham, NH. The investigators will exchange preliminary data from this summer's work, help to develop the core processing line, and discuss plans for 1990, 1991, etc. 6. "Masthead" The GISP2 Notebook is published by the GISP2 Science Management Office at The Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824-3525. The GISP2 Science Management Office is the coordinating office for the GISP2 project. It is responsible for coordinating scientific and logistical activities. Paul Mayewski is the Director of the SMO and Michael Morrison is the Associate Director. Direct correspondance to: Michael Morrison GISP2 Science Management Office Institute for the Study of Earth, Oceans, and Space University of New Hampshire Durham, NH 03824-3525 and Phone: 603-862-1991 Fax: 603-862-2124 OMNET: "GISP2" Two committees provide oversight of GISP2: Advisory Committee Charles Bentley Wallace Broecker John Imbrie Executive Committee Pieter Grootes Paul Mayewski (Chairman) Martin Wahlen 7. Acknowledgements Permission to work in Greenland is generously provided by The Commission for Scientific Research in Greenland and the governments of Denmark and Greenland and is gratefully acknowledged. GISP2 is made possible by the efforts of: The 109th Air National Guard from Scotia, NY providing ski-equipped C-130 airlift support; The National Science Foundation, Division of Polar Programs providing funding for the individual science projects and the GISP2 Science Management Office (Grant No. DPP-8944997); Harold Borns, Peter Wilkness, and Herman Zimmerman of NSF DPP providing support for GISP2 at NSF; the Polar Ice Coring Office at the University of Alaska providing logistical and drilling support; and the scientific colleagues of Eurocore and GRIP with whom collaboation and cooperation have been most profitable. Finally, thanks go to the PICO drillers, GISP2 camp staff and Sondrestrom staff who have made this first season work. Draft: Page: